The goals of this amended program project application are directed towards the immunobiology of normal and neoplastic lymphocytes, the role of the major histocompatibility complex (MHC) in immune regulation, and the cytogenetics and biology of human lymphoid tumors. Specifically, the component project deals with studies of (1) the function and specificity of human and murine T cells, (2) the control by MHC gene products of replication of leukemogenic virus in cultured cell lines, and (3) the genetic and biologic changes associated with human lymphocytic leukemia. This program is a component of the University of Pennsylvania Cancer Center.